The invention relates to a ball bearing with an inner race and an outer race disposed coaxially with respect to it, and between inner race and outer race bearing balls are disposed, which are guided by means of a cage, the cage being comprised of a composite material.
Such ball bearings have been and are currently employed in many areas of technology. In doing so, it has been found that in most cases the ball bearing cage is the structural element limiting the service life of the ball bearing. This can be explained by the fact that the cage is exposed to enormous force actions. It is alternately or simultaneously in contact with the rapidly rotating balls as well as with the inner race and/or the outer race, with the inner race and/or the outer race also rotating about a rotational axis. Especially at high rotational speeds of one of the races of approximately 500,000 rotations per minute, cages of conventional composite materials in the long run do not bear up under these loadings. Especially difficult is the use of conventional composite material in applications, in which the ball bearing is at least for a time exposed to increased temperatures, increased pressure and increased air humidity. In particular ball bearings in medical technology must be capable of resisting these conditions, since the devices with the ball bearings must frequently be autoclaved. For this process is specified a pressure of 1 bar, a temperature greater or equal to 134EC, as well as a saturated vapor atmosphere over a time period of approximately three minutes. Ball bearing cages of conventional composite material, such as phenolic resin in combination with cotton fibers, do not withstand these conditions at all or not for very long.
Disintegration processes occur, which result in the destruction of the entire ball bearing.
Ball bearing cages comprised of PEEK (polyether ether ketone) or PI (polyimide) or PAI (polyamide imide) have therefore been developed. However, ball bearing cages of one of these materials have the disadvantage that they do not have any properties which allow operation after lubrication system failure. In contrast to the known composite materials of phenolic resin and cotton fibers, the listed cage materials do not contain any fibers, such that no lubricant can be stored in the cage itself. This leads to the immediate destruction of the ball bearing if there is no more lubricant available in the ball bearing. However in such situations, ball bearing cages of phenolic resin and cotton fibers output small quantities of the stored lubricant to the running faces and/or to the balls, such that the service life of the ball bearing can be significantly extended. As already stated, ball bearings with a ball bearing cage of phenolic resin and cotton fibers have however the disadvantage that they only conditionally withstand the loadings to which a ball bearing, in particular in medical technology, is exposed.
The invention is based on the task of proposing a ball bearing which combines long service life with the properties of being capable of operating after a lubrication system failure.